The identification and taxonomy of Leptospira are based on the antigenic composition of their cell surface components. In addition, antibodies which react with one or more of the surface antigens are responsible for immunity to leptospirosis. The antigenic composition of the leptospires is complex. There are over 160 serovars (antigenic types) and many of these have overlapping antigenic properties. As a result of this the definitive identification is difficult, time consuming and can only be conducted at specialized laboratories. If serovar specific antigens and antisera were available the identification of leptospires would be greatly facilitated and could be conducted by the smaller diagnostic laboratories. Our objectives are to: 1) isolate and purify the genus-specific, serovar-specific and protective antigens of Leptospira; 2) develop a serovar and genus-specific hemagglutination test; 3) study in vivo antigen variation of leptospires; 4) study role of phagocytosis in leptospirosis; and 5) develop and evaluate leptospiral isolation media.